1. Field of the Invention
The present invention relates to electronic amplifiers, and more particularly, to higher efficiency heterojunction bipolar transistor amplifiers.
2. Description of Related Art
In the present era of expanding wireless communication, it is highly desirable to increase the efficiency of high power amplifier devices, especially in the radio frequency (RF) range of operation. Increased efficiency generally leads to improved amplifier reliability, as well as providing for the use of smaller amplifier devices and smaller, more portable power supplies. These features are preferred in developing products such as, for example, mobile transceivers for wireless communication, phased array radar systems, or satellites with reprogrammable antenna beam patterns.
Heterojunction bipolar transistor (HBT) devices are one type of amplifier commonly used in RF wireless communication. HBTs have been built in monolithic microwave integrated circuits to perform as RF amplifiers. Conventional HBTs usually have a structure employing a uniform, single layer collector region. Conventional HBT devices operate at relatively low efficiencies, that is, a relatively low portion of the power supplied to the amplifier is usefully delivered to the output signal, with the remaining portion of the total input power being dissipated as heat. Low efficiency HBTs use more power, are relatively unreliable, dissipate a greater portion of the input power as heat, are generally larger in size amplifiers and generally operate from and require larger power supplies.
Accordingly, a need exists for increasing the efficiency of high power amplifier devices, especially in the RF range of operation.